Make CustomElementSchedular static

Source/core/dom/custom/CustomElementScheduler.h

Index: Source/core/dom/custom/CustomElementScheduler.h
diff --git a/Source/core/dom/custom/CustomElementScheduler.h b/Source/core/dom/custom/CustomElementScheduler.h
index 68ba526a0a27e1f25945c4141e846c39d367b0b9..976679d41b1c27436e4d1b6af062e53b637a2743 100644
--- a/Source/core/dom/custom/CustomElementScheduler.h
+++ b/Source/core/dom/custom/CustomElementScheduler.h
@@ -62,26 +62,10 @@ public:
     static void microtaskDispatcherDidFinish();
     static void callbackDispatcherDidFinish();
 
-    void trace(Visitor*);
-
 private:
     CustomElementScheduler() { }
 
-    static CustomElementScheduler& instance();
     static void enqueueMicrotaskStep(Document&, PassOwnPtrWillBeRawPtr<CustomElementMicrotaskStep>, bool importIsSync = true);
-
-    CustomElementCallbackQueue& ensureCallbackQueue(PassRefPtrWillBeRawPtr<Element>);
-    CustomElementCallbackQueue& schedule(PassRefPtrWillBeRawPtr<Element>);
-
-    // FIXME: Consider moving the element's callback queue to
-    // ElementRareData. Then the scheduler can become completely
-    // static.
-    void clearElementCallbackQueueMap();
-
-    // The element -> callback queue map is populated by the scheduler
-    // and owns the lifetimes of the CustomElementCallbackQueues.
-    typedef WillBeHeapHashMap<RawPtrWillBeMember<Element>, OwnPtrWillBeMember<CustomElementCallbackQueue> > ElementCallbackQueueMap;
-    ElementCallbackQueueMap m_elementCallbackQueueMap;
 };
 
 }